CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

The structures of the hydrated cluster, CO • 3 ⎯.nH 2 O (n=1-8) are calculated at
B3LYP/6-311++G(d,p) level of theory and discussed in Chapter 2. Similarly various
possible initial structures of CO •− 3 .nH 2 O (n=1-8) clusters are considered for global
geometry optimization and a number of minimum energy structures (conformers) are
obtained. Fully optimized global minimum energy structure of each size of hydrated
cluster, CO •− 3 .nH 2 O (n=1-8) at B3LYP/6-311++G(d,p) level is displayed in Fig. 5.2.
These structures of the hydrated cluster, CO • 3 ⎯.nH 2 O are very close to that discussed in
Chapter 2.
It is observed that CO • 3 ⎯.nH 2 O clusters are stabilized by double hydrogen bonding
(DHB), single hydrogen bonding (SHB) as well as inter water hydrogen bonding (WHB).
In each case, the distance between the C and O atoms of carbonate moiety (CO • 3 ⎯) is ~
1.3 Å. The calculated distance between O (of CO • 3 ⎯) and H-bonded H atoms is 1.8-2.2 Å
(SHB and DHB bond) and the distance between O and H atoms in inter water network is
1.9-2.1 Å (WHB bond). It is worth to mention that the globally optimized structures for
both the cases are very close to that of most stable structure as discussed in Chapter 2.
5.3.2. UV-Vis Spectra
Calculations are performed to find out a few low lying excited states for all the
solvated clusters as well as for the isolated dimer radical anion (Cl •− 2 ) at both CIS and
TDDFT level of theory to observe the shift in optical absorption wavelength (l) of the
dimer radical anion (Cl •− 2 ) with addition of solvent water molecules. The absorption
maxima (λ max ) for isolated dimer radical anion (Cl •− 2 ) is found to be at 437 nm at CIS/6-
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